The word τελέω (from τέλος, 'end') is ‘to accomplish anything by bringing it to an end.' So the Lord was straitened until His death was accomplished. Luke 12:50. Comp. chap. 18:31 and John 19:28; and for the general sense of the word, Matt. 11:1; Rev. 10:7; 11:7.
υελειόω (from τέλειος,, ‘perfect') is ‘to make perfect, complete,' not merely to bring to an end. See John 17:23; Heb. 2:10; 5:9; 10:1; 11:40; Jas. 2:22. In Acts 20:24 the apostle Paul uses it of ‘completing' his course.
πληρόω (from πλήπης, 'full') signifies to fill, fill up, fulfill.' The Lord said that He did not come to abolish, or make void, the law and the prophets; He came to fulfill, or give the fullness to them ― to make good the whole scope of the law and the prophets. Matt. 5:17. This helps as to the force of Col. 1:25: not only was the circle of truth, the communication of God's mind, as to the subjects of revelation, complete when the doctrine of the assembly was brought out through the apostle; but the truth as to the mystery gave fullness to the whole revelation of God. See also Matt. 1:22; 2:15, 17, 23, and many other passages. In the sense of ‘filling' see Luke 2:40; the house was filled with the scent of the ointment in John 12:3; and the house was filled with the sound, in Acts 2:2.
The apostle prays that the Ephesian saints might be filled unto all the fullness of God. Eph. 3:19; and in 4:10 we read "He that descended is the same that has also ascended up far above all the heavens that he might fill all things."
For ‘filling up' see Matt. 23:32.